#define _CRT_SECURE_NO_WARNINGS	

#include<stdio.h>

int main()
{
    int n;
    scanf("%d", &n);
    double sum = 0;
    for (double i = 1; i <= 2 * n; i++)
        sum += 1 / i;
    printf("%.6lf", sum);
    return 0;
}